Intracellular bacterial pathogens secrete proteins after infection that function to alter the normal structural and metabolic machinery of the host cell thus facilitating their survival and avoidance of host immune surveillance. Recent discoveries of the molecular mechanisms that intracellular bacterial pathogens use for evasion or subversion of the immune system of the host will greatly facilitate the development of antibacterial vaccines and diagnostic tools. Much like many other intracellular facultative pathogens such as Salmonella typhimurium, Mycobacterium tuberculosis and Legionella pneumophila, F. tularensis shares a predilection for macrophages as its preferred host cell. However, in contrast to other intracellular bacterial pathogens, little is known about virulence factors used by F. tularensis internally within its host cell. We have designed and tested a system that enables us to identify Class I Accessible Proteins (CAPs) in Salmonella typhimurium and propose to utilize a similar approach for the study of F. tularensis. Due to their susceptibility to the host' s processing and presentation pathways, CAPs represent a potentially important resource for the design and construction of effective vaccines against F. tularensis.